The objectives of the proposed investigation are to develop generalized, finite element modeling techniques and materials characterization procedures which may be used to analyze failure patterns and degenerative processes in musculoskeletal structures. These approaches will be used to model the mechanics of normal and degenerative knee joints and to explain failure processes in current total joint replacements. The methods will also be used to systematically study the etiology of degenerative arthritis, the mechanics of therapeutic procedures and the improvement of joint replacement techniques. Our previous finite element models of the knee have emphasized the controlling influence of trabecular bone density in both normal and pathological joint stress distributions. Accordingly, we will use computerized tomography (CT) to determine in-situ the spatial variations in trabecular density and will attempt to directly couple the finite element modeling procedures with CT scans. The work is organized into phases on: 1) materials characterization; 2) finite element modeling; and 3) verification including quantitative morphology. The materials characterization phase is designed to provide input data for the finite element models and to develop experimental and clinical techniques for the study of normal and diseased tissue. In particular, we will measure the spatial variation in the viscoelastic properties of articular cartilage in the knee and will develop multiaxial failure theories for trabecular bone for input to the finite element models. The post-yield energy absorption capacity of trabecular bone will be quantitatively characterized and new data will be developed for the shear strength and fatigue life of PMMA and PMMA-trabecular bone interfaces.